a. Field of the Invention
The instant invention relates to assemblies and methods for puncturing, or piercing, tissue within the body, including, for example, transseptal access systems and methods for accessing the left atrium from the right atrium by crossing the fossa ovalis. In particular, the instant invention is directed towards transseptal puncture needles and transseptal puncture needle assemblies.
b. Background Art
The human heart includes a right ventricle, a right atrium, left ventricle and left atrium. The right atrium is in fluid communication with the superior vena cava and the inferior vena cava. The tricuspid valve separates the right atrium from the right ventricle. The mitral valve separates the left atrium from the left ventricle. The right atrium is separated from the left atrium by the interatrial septum.
A wide variety of diagnostic and therapeutic procedures have been developed in which a catheter is transluminally advanced within a guide sheath or over a guidewire into various chambers and across valves of the heart. The most difficult chamber of the heart to access with a catheter is the left atrium. Access to the left atrium through the pulmonary artery is not possible. Approaches from the left ventricle are difficult, may cause arrhythmias, and may present difficulty in obtaining stable catheter positioning. Accordingly, the most common approach used by electrophysiologists to gain access to the left atrium is through puncture of the interatrial septum from the right atrium.
The objectives of left atrial access can be either diagnostic or therapeutic. One therapeutic use is electrophysiological intervention (e.g., left atrial ablation). Catheter ablation involves the placement of energy (often RF energy) through a catheter, into various locations of the heart to eradicate inappropriate electrical pathways affecting the heart function. When these locations are in the left atrium, the catheter through which the RF generator is placed typically is itself placed through transseptal catheterization.
Transseptal puncture needles are used by physicians who perform specialized invasive cardiology techniques. For example, it is known to access the left atrium using a transseptal approach for catheter ablation of arrythmogenic tissue. During such an approach, a physician may use a transseptal introducer and a long, curved needle for left atrial access from the venous system. The introducer, which may be curved to facilitate access to a desired portion of the left-heart anatomy, includes a sheath and may include a separate dilator. The curved needle may be, for example, a stainless steel Brockenbrough curved needle or a trocar.
The curved needle is used to make the transseptal puncture after the curved transseptal introducer is used to guide the needle into position. In particular, once the transseptal introducer is in the right atrium, the distal tip of the guiding introducer is positioned against a puncture site, such as the fossa ovalis in the inter-atrial septal wall. The Brockenbrough needle is then advanced distally through the transseptal introducer beyond the distal end of the introducer until it punctures the fossa ovalis. If the introducer includes a dilator, the dilator may be advanced with a needle through the punctured fossa ovalis to prepare an access port through the septum and into the left atrium. Once the sheath has been seated across the septum and in the left atrium, the dilator, if present, and the needle may be withdrawn from the sheath. This sheath then provides lumenal access into the left atrium for direct insertion of, for example, a treatment or diagnostic catheter.
To facilitate insertion of the curved needle through the curved transseptal introducer, a stylet may be inserted into the cannula of the needle. The stylet is a flexible rod that stiffens the curved needle and gives it form during its passage through the curved transseptal introducer.
In order to minimize the risk of inadvertently puncturing the left atrial wall just after crossing the septum, it is important that the transseptal puncture needle is sufficiently sharp to reduce the amount of insertion force required. One of ordinary skill in the art can appreciate that, if excessive force is required to insert the needle through the introducer or to puncture the inter-atrial septum, the transseptal puncture needle may inadvertently puncture the atrial free wall, the aorta, the inferior vena cava, or the coronary sinus, for example.
On the other hand, if the needle is too sharp, it may not provide sufficient feedback to the surgeon to let the surgeon know when the needle pierces the inter-atrial septum. In addition, advancement of a sharp needle tip or a needle tip with a sharp edge through the dilator or sheath may cause particles to be skived from the interior surface of the dilator or sheath. Accordingly, it is desirable that the transseptal puncture needle strike a balance between sufficiently sharp to reduce the amount of insertion force required while not so sharp as to cause skiving and/or to provide too little feedback to the surgeon.